Usually they will charge to get your catch, but this is one of the few times I have seen them come all the way in.
For me the key is keeping your catch really close to your chest. Usually once you get it in close to you, within bear hug radius, they don't want any part of it. They will circle you, even charge to test you, but they usually spin off once you make eye contact. If you leave your stringer dangling off the back of you then I have seen them come all the way and strike the stringer. But if its in front of you and the shark is in your line of sight they won't charge all the way in, from what I have seen. But if you give them the opportunity to sneak up behind you then they will usually take it.
I would be curious to see what happened before this, and know what kind of fish he had. They seem to go a lot more crazy over the exotic fish, like Permit and African Pompano. Snapper and grouper not so much.